The invention relates to a mask for covering the outer margin of a disk-shaped substrate surface during a coating process, such as a sputtering or vapor-coating process in a vacuum.
Machine-readable data storage devices for a great variety of applications are gaining in importance. Depending on the use and the required data storage device density, a distinction is made of magnetic, magneto-optical and optical data storage devices, such as hard disks, floppy disks, magnetic tape and CD's. All data storage devices have it in common that at the midpoint of their manufacture is a vacuum process for the application of technical coatings.
What is involved essentially in the present invention is the manufacture of magneto-optical and optical data storage devices. As the base for these storage devices disk-shaped substrates of plastic, such as polycarbonate (PC) or polymethyl methacrylate (PMMA), are used. During the application of the data storage coatings to these substrates, areas of the substrate surface are masked off. As a rule, masks for this purpose are used which mask off the inner and/or outer area of the substrate surface. These masks are often disposed so as to be stationary in front of the particular coating sources. The substrates to be coated are placed on these stationary masks by a handling system.
The diameters of the disk-shaped substrates are standardized and are substantially between 80 and 300 mm. A new generation of data storage devices is characterized by diameters that are smaller than 80 mm. This reduction of the diameter necessarily results in a reduction of the storage surface available on the substrate. The manufacturers of such data storage devices try to make optimum use of the usable storage area. They therefore strive to make the masked areas as small as possible and to minimize the coaxiality tolerances, especially of the outside mask.
Coating apparatus with a plurality of stations constitute a special problem. If the substrates are coated successively in many stations, and the user permits only a very small eccentricity of the inside and outside masking, then it is often impossible to achieve this with permanently built-in, stationary mask systems.